combustion

ABSTRACT

A process of improving the oxidation of carbonaceous products derived from the combustion of fuel and improving combustion of a fuel is described. The process comprises adding to the fuel before combustion thereof a composition comprising at least an organo-metallic complex of a Group I or Group II metal characterized in that the concentration of the complex in the fuel before combustion is 30 ppm or less.

The present invention relates to a process for improving the oxidationof carbonaceous products derived from the combustion or pyrolysis offuel (such as with the use of a particulate trap for use with dieselengines) and/or for improving the combustion of fuel.

Products from the combustion or pyrolysis of diesel fuels include carbonmonoxide, nitrous oxides (NO_(x)) unburnt hydrocarbons and particulates.Particulates are becoming increasingly regarded as serious pollutants,in that there is a growing recognition of the health risks associatedwith particulates emissions. These particulates include not only thosewhich are visible as smoke emission, but also unburned and partiallyoxidised hydrocarbons from fuel and the lubricants used in dieselengines.

Diesel engines are prone to emission of high levels of particulatematter when the engine is overloaded, worn or badly maintained.Particulate matter is also emitted from diesel engines exhausts whenengines are operated at partial load although these emissions arenormally invisible to the naked eye. The unburned or partially oxidisedhydrocarbons also emitted to the atmosphere are irritant astringentmaterials. Further, in a problem recently highlighted for diesel fuel,emissions of particulate matter of less than 10 micrometers principledimension ("PM10 matter") , is claimed to cause 10,000 deaths in Englandand Wales and 60,000 deaths in the USA annually, as published in the NewScientist, March 1994, p12. It is suspected that these smaller particlespenetrate deeply into the lung and lodge.

As indicated, particulate emission by diesel engines is a major sourceof harmful atmospheric pollution, and an effective method to controlparticulate emissions from diesel engines is highly sought after.Legislation now exists in many countries of the World designed tocontrol pollution from diesel engines. More demanding legislation isplanned.

Prior activity in the area of reducing the level of particulates may beregarded as using one of two strategies: engine design and managementsolutions or trap oxidation solutions.

Engines that have been developed to achieve low levels of emission arewell known to those familiar with the art and examples of such designsare given in S.A.E. International Congress (February 1995) S.A.E.Special Publication SP-1092. The drawbacks to the various enginemanagement solutions include cost, complexity and the poor capabilityfor retrofitting.

Traps fitted to diesel engines have been proposed as a solution butthese normally require some external energy input for regeneration. Suchdevices are well known to those familiar with the art and some examplesare discussed in "Advanced techniques for thermal and catalytic dieselparticulate trap regeneration", SAE International Congress (February1985), SAE Special Publication-42 343-59 (1992) and S.A.E. InternationalCongress (February 1995) and S.A.E. Special Publication SP-1073 (1995).In addition to the need for supplying an external heat source, the trapoxidation solutions suffer from similar problems. They are also prone tocause trap blockage and/or `chimney fires` resulting from sudden andintense burnoff of soot from highly loaded traps.

Catalytic devices can assist the control of emissions from dieselengines but require low sulphur fuel (<500 ppm) to enable benefits toexhaust emission to be achieved.

Additives can be used to contribute to both strategies. In enginemanagement approaches, there is a well-known trade-off between NO_(x)and particulates emissions. Diesel engines emissions tests now includespecified levels for all pollutants. An additive which achieves someuseful level of particulates suppression to some extent decouples thistrade off, thereby giving the engineer more freedom to achieve poweroutput or fuel economy within a given emission standard.

The use of metal-based additives within diesel fuels for these ends arewell known. However, the known additives can present a number ofdrawbacks.

For example, some previous solutions have overlooked the consequence ofthe potential for emissions of the metals from the engine or the trap.Even the best of traps cannot be 100% efficient at trapping particlesand therefore some metal will be emitted. As a consequence, where toxicmetals are employed, it must always be doubtful that an overallemissions benefit is so obtained. In addition, previous attempts haveused relatively high dose rates of metals, typically of the order of50-100 ppm or more. This has several drawbacks as a greater mass ofsolids may ultimately be emitted by the engine and a more rapid blockageof a trap may thus result. Unwanted deposits may also be formed withinthe engine, ultimately to the detriment of performance. Furthermore,previous attempts have used metals which give combustion or pyrolysisproducts, or yield species within the trap that are both involatile andof low or very low water solubility. As a consequence, blockage of theexhaust system, or more likely the oxidation trap, leads to a need fordisposal or expensive recycling of the trap. Also, previous attemptshave used additive metals which may give rise to products antagonistictowards the trap or exhaust system components.

WO-A-94/11467 to Platinum Plus discloses the use of platinum compoundsin conjunction with a trap to lower the unburned hydrocarbon and carbonmonoxide concentration of diesel exhaust gases. Lithium and sodiumcompounds are also claimed to be useful in lowering the regenerationtemperature of the trap. No engine data is supplied in support of thisclaim. The teaching of this patent is that lithium and sodium organicsalts are available and suitable for use to the extent that they arefuel soluble and are stable in solution. There is no suggestion that anysalt of a given metal performs better than any other salt of that metal.

WO-A-92/20762 to Lubrizol describes an array of chelatingfunctionalities with an extensive range of metals as fuel additivescapable of lowering the ignition temperature of particulates caughtwithin a trap. No engine data is given to support this contention.Example complexes are given for copper only. The Application teaches theuse of an antioxidant additive in conjunction with the metal complex tobe essential. No evidence is given that the complexes are effective inthe absence of this additive, that alkali or alkaline earth metals areat all effective, nor that any one fuel soluble and stable complex orsalt may perform differently to any other.

DE-A-40 41 127 to Daimler-Benz describes the use of various fuelsoluble, stable lithium and sodium salts in reducing the ignitiontemperature of the mateial retained within a diesel particulate filter.Frequent partial unblocking of the filter is observed at sodium levelsof around 32 ppm m/m, 28 ppm m/m with lithium. There is no suggestionthat any one fuel soluble, stable salt performs better than any other;in fact, the examples given stress the similarity of the resultsobtained between one additive and another.

WO-A-95/04119 to Associated Octel describes the use of Lewis basecoordinated alkali and alkaline earth metal salts in reducing dieselengine exhaust emissions. The salt complexes have the advantage of beingfuel soluble and stable. The Application contains some speculation thatsuch additives may be effective to catalyse the oxidation of trappedparticulates. However, it presents no evidence to support this, andfurther, does not teach that any one additive may be any more effectivethan any other.

DE-A-20 29 804 to Lubrizol discloses the use of oil soluble carboxylicdispersants to reduce the formation of deposits on inlet valves. Thereis no suggestion that the additives may remove previously formeddeposits. The teaching is that any emissions benefit arises purely frommaintaining the cleanliness and, as a result, the designed function ofthe engine.

EP-A-207 560 to Shell concerns the use of succinic acid derivatives andtheir alkali or alkaline earth metal (especially potassium) salts asadditives for increasing the flame speed within spark ignition internalcombustion engines. However, there is no teaching regarding the use ofsuch additives in compression ignition engines.

EP-A-555 006 to Slovnaft AS discloses the use of alkali or alkalineearth metal salts of derivatised alkenyl succinates as additives forreducing the extent of valve seat recession in gasoline engines designedfor leaded fuel but used with non-leaded.

GB-A-2 248 068 to Exxon teaches the use of additives containing analkali, an alkaline earth and a transition metal to reduce smoke andparticulate emissions during the combustion of diesel fuel. According tothe teaching of this document, the presence of a transition metal isessential. There is no teaching regarding efficacy for trapregeneration, or that any one salt of a given metal performs better thanany other.

EP-A-0 476 196 to Ethyl Petroleum Additives teaches the use of a threepart composition including a soluble and stable manganese salt, a fuelsoluble and stable alkali or alkaline earth metal and a neutral or basicdetergent salt to reduce soot levels, particulates, and the acidity ofcarbonaceous combustion products. There is no suggestion that anyparticular fuel soluble, stable alkali or alkaline earth metal additiveperforms better than another.

EP-A-0 423 744 teaches the use of a hydrocarbon soluble alkali oralkaline earth metal containing composition in the prevention valve seatrecession in gasoline engines designed for leaded but run on unleadedfuel. There is no teaching in this document relevant to dieselcombustion.

The present invention seeks to improve the combustion of diesel fuel inan engine combustion chamber but primarily to provide an additive whichcatalyses the oxidation of soot within the trap thereby reducing theso-called `light off temperature`. In particular the present inventionseeks to overcome one or more of the problems associated with the knownfuel additives.

According to a first aspect of the present invention there is provided aprocess for improving the oxidation of carbonaceous products derivedfrom the combustion or pyrolysis of fuel (such as with the use of aparticulate trap for use with diesel engines), the process comprisingadding to the fuel before the combustion thereof a compositioncomprising at least an organo-metallic complex of a Group I metal or atleast an organo-metallic complex of a Group II metal, or a mixturethereof, characterised in that the concentration of the metal of theGroup I and/or the Group II organo-metallic complex in the fuel beforecombustion is 100 ppm or less preferably 30 ppm or less ; and whereinthe organo-metallic complex induces acceptable spontaneous trapregeneration according to the Test Protocol presented in the Examples.The process may additionally improve combustion of the fuel.

According to a second aspect of the present invention there is provideda use of an organo-metallic complex as defined in the first aspect ofthe present invention for improving combustion of fuel and/or improvingthe oxidation of carbonaceous products derived from the combustion orpyrolysis of fuel (such as with the use of a particulate trap for usewith diesel engines), wherein the complex is added to the fuel beforethe combustion thereof and wherein the concentration of the metal of theGroup I and/or the Group II organo-metallic complex in the fuel beforecombustion is 100 ppm or less, preferably 30 ppm or less, morepreferably 10 ppm or less, yet more preferably 5 ppm or less.

Many types of particulate traps are known to those skilled in the artincluding as non-limiting examples `cracked wall` and `deep bed` ceramictypes and sintered metal types. The invention is suitable for use withall particulate traps; the preferred concentration of metal in the fuelis a function of trap design, probably surface area to volume ratio. Fora `deep bed` filter trap, such as one constructed from 3M Nextel™ fibre,the concentration of metal in the Group I and/or Group II metal complexin the fuel is more preferably 30 ppm or less. For a ceramic monolithtype or `cracked wall` type filter trap, such as the Corning EX80™, theconcentration of metal in the Group I and/or Group II metal complex inthe fuel is more preferably 30 ppm or less.

The key advantages of the present invention are that the composition canachieve improved regeneration of traps (such as diesel engineparticulate traps) and/or improved combustion in engines (such as dieselengines) at low dosages in the fuel. Further advantages are that theadditive is readily fuel soluble and can be provided at highconcentrations in fuel miscible solvent. Yet a further advantage is thatthe additives are particularly stable with respect to water and thusresistant to water leaching. The invention thus provides a compositionthat is very compatible with fuel handling, storage and delivery. Inparticular, diesel often encounters water, especially during delivery tothe point of sale, and so leaching resistant or stable compositions arebeneficial.

The low dosage aspect is particularly advantageous as the presentinvention utilises metals of known low toxicity, and preferably thosethat are essential to life and are widely prevalent in the environment.

A particular advantage of the composition for use in the presentinvention is that it provides an additive which catalyses the oxidationof soot within the trap thereby reducing the so-called `light offtemperature` and/or improves the combustion of diesel fuel.

Thus important advantages of the present invention include thecost-efficient preparation of a diesel fuel additive having high fuelsolubility and stability, which when burned with the fuel: reduces theignition temperature and/or enhances oxidation of resulting particulatematter caught within a trap, may render the particulate matter remainingin the exhaust gas more collectable on a trap and/or reduces theemission of soot, unburned hydrocarbons and partially oxidisedhydrocarbons--when compared to that of a fuel burned without theadditive preparation. In this context `regeneration` is defined as theprocess of reducing the pressure drop across the filter trap through theoxidation of trapped material. This normally requires some externalenergy input. Such filter trap devices and their means of regenerationare well known to those familiar with the art and some examples arediscussed in "Advanced techniques for thermal and catalytic dieselparticulate trap regeneration", SAE International Congress (February1985) SAE Special Publication-42 343-59 (1992). However, use of thecomposition according to the present invention reduces or eliminates theneed for an external energy intput.

Another important advantage of the present invention is that under manyengine operating conditions as a result of the addition of the complexto the fuel, there is less particulate matter and less remainingparticulate matter. Hence the trap takes longer to fill with particulatematter. The frequency at which traps must be regenerated is thusreduced. Furthermore, the need for energy from an external source to aidregeneration can be reduced or eliminated.

Thus important advantages of the present invention include the provisionof a fuel additive that when burned with the fuel: reduces the emissionof soot, unburned hydrocarbons and partially oxidised hydrocarbons;renders the particulate matter remaining in the exhaust gas morecollectable on a trap; reduces the ignition temperature of the trappedmaterial; enhances the oxidation of the trapped particulates--whencompared to that of fuel burned without the additive preparation.

The burning of soot and other hydrocarbons from the surfaces of a trapfollowing the combustion or pyrolysis of fuel comprising the compositionof the present invention therefore provides a way to regenerate thefilter and so prevent the unacceptable clogging of diesel particulatetraps.

Also, the fuel additive of the present invention leads to reduced levelsof combustion or pyrolysis ash. Thus, clogging of the trap from theadditive residue is kept to a minimum.

Preferably for a `deep bed` filter trap, such as one constructed from 3MNextel™ fibre, the concentration of metal in the Group I and/or Group IImetal complex in the fuel is 30 ppm or less.

Preferably, for a `cracked wall` type filter trap, such as the CorningEX80™, the concentration of metal in the Group I and/or Group II metalcomplex in the fuel is 30 ppm or less.

Preferably, the organo-metallic complex is stable to hydrolysis.

Preferably, the organo-metallic complex comprises a Lewis base.

Preferably, the organo-metallic complex comprises a Lewis base and theorgano-metallic complex is a metal complex of any one of the followingorganic compounds:

a) an aliphatic alcohol of the general formula CH₃ --X--OH, where Xsignifies a C₁₋₈ alkyl group, or a compound of such an alcohol;

b) an aromatic alcohol of the general formula Ph--X--OH where Phsignifies a phenyl ring, X signifies a C₁₋₈ alkyl group;

c) an ortho, meta or para singly substituted phenol wherein thesubstituted group is a C₁₋₈ alkyl group;

d) an aliphatic carboxylic acid of the general formula CH₃ --X--COOH,where X signifies a C₃₋₁₆ alkyl group, or an isomeric compound of such acarboxylic acid; or

e) a 1-naphthoic acid, a 2-naphthoic acid, a phenyl acetic acid or acinnamic acid.

In an alternative embodiment, preferably the organo-metallic complex isa metal complex of any one of the following organic compounds: asubstituted aliphatic alcohol, a substituted or unsubstituted aliphatichigher alcohol (e.g. a diol), a substituted aromatic alcohol, asubstituted phenol comprising at least two substituted groups, asubstituted aliphatic carboxylic acid, a substituted or unsubstitutedaliphatic higher carboxylic acid (e.g. a dicarboxylic acid) or asubstituted or unsubstituted aromatic acid, or derivatives thereof, butnot 1-naphthoic acid, 2-naphthoic acid, a phenyl acetic acid or acinnamic acid.

Preferably, the organo-metallic complex is a metal complex of any one ofthe following organic compounds: a substituted aliphatic alcoholcontaining ether (eg --OCH₂ CH₂ --) or amino groups, a substituted orunsubstituted aliphatic higher alcohol (eg a diol) containing ether (eg--OCH₂ CH₂) or amino groups, a substituted aromatic alcohol containinggroups capable acting as Lewis base ligands (eg --NR₂ or --OR) and beingin a position to form dative bonds to a metal bound to the alkoxy group,a substituted phenol comprising at least two substituted groups, asubstituted phenol containing groups capable acting as Lewis baseligands (eg --NR₂ or --OR) and being in a position to form dative bondsto a metal bound to the phenol hydroxy group, an aliphatic carboxylicacid of the general formula CH₃ --X--COOH where X signifies an alkylgroup with 17 or more carbon atoms or is a C₃₋₁₆ alkenyl group orisomeric compounds of such, an aliphatic carboxylic acid R¹ R² R³ CCOOHwherein R¹, R² and R³ are independently selected from hydrogen, alkyl oralkenyl groups containing two or more carbon atoms but wherein no morethan one R is hydrogen and excluding aliphatic carboxylic acids offormula CH₃ --X--COOH where X signifies a C₃₋₁₆ alkyl or alkenyl group,a carboxylic acid R¹ R² R³ CCOOH wherein at least one R is aryl orsubstituted aryl and the others may be H, alkyl or alkenyl groups,except where the carboxylic acid is phenyl acetic acid, a substituted orunsubstituted aliphatic higher carboxylic acid (eg a dicarboxylic acid)preferably an alkyl or alkenyl substituted succinic acid, the product ofreaction of a metal hydroxide with a substituted or unsubstitutedaliphatic or aromatic anhydride, preferably a succinic anhydride, or aβ-diketone, substituted β-diketone or β-keto acid.

Preferably, the organo-metallic complex is a metal complex of a highlysubstituted phenol (e.g. di-(t.butyl)methylphenol).

Preferably, the organo-metallic complex is fuel soluble.

Preferably, the organometallic complex is soluble in a fuel-compatiblesolvent such that the organometallic complex is soluble to the extent of10 wt %, preferably 25 wt % and most preferably 50 wt % or more in thesolvent. Preferably some or all of the solvent may be a polybutene.

Preferably, the organo-metallic complex is of the formula M(R)_(m).nLwhere M is the cation of an alkali metal or an alkaline earth metal, ofvalency m, not all metal cations (M) in the complex necessarily beingthe same; R is the residue of an organic compound RH, where R is anorganic group containing an active hydrogen atom H replaceable by themetal M and attached to an O, S, P, N or C atom in the group R; n is apositive number indicating the number of donor ligand molecules forminga bond with the metal cation, but which can be zero; and L is a speciescapable of acting as a Lewis base.

Viewed from a further aspect the invention provides a process ofregenerating a particulate trap use for entrapping particulates in anexhaust gas, the process comprising burning off the trapped particulatesin and on the particulate trap; characterised in that at least some ofthe particulates comprise an organo-metallic complex of the formulaM(R),.nL or a compound derived from the combustion or pyrolysis of sucha complex in fuel wherein M is the cation of an alkali metal, analkaline earth metal, or a rare earth metal of valency m, not all metalcations (M) in the complex necessarily being the same; R is the residueof an organic compound RH, where R is an organic group containing anactive hydrogen atom H replaceable by the metal M and attached to an O,S, P, N or C atom in the group R; in a positive number indicating thenumber of donor ligand molecules forming a bond with the metal cation,but which can be zero when R comprises L; and L is a species capable ofacting as a Lewis base; further wherein the regeneration is capable ofoccurring at milder conditions (such as at a lower exhaust gastemperature) than when the particulates do not comprise either theorgano-metallic complex or the combustion or pyrolysis products thereof.

Preferably, R and L are in the same molecule, in which case L isconveniently a functional group capable of acting as a Lewis base.

Preferably, the composition is dosed to the fuel at any stage in thefuel supply chain.

Preferably the composition is added to the fuel close to the engine orcombustion systems, within the fuel storage system for the engine orcombustor, at the refinery, distribution terminal or at any other stagein the fuel supply chain.

The present invention therefore relates to additives for liquidhydrocarbon fuel, and fuel compositions containing them.

The term "regenerating a particulate trap" means cleaning theparticulate trap so that it contains minimal or no particulates. Theusual regeneration process includes burning off the trapped particulatesin and on the particulate trap. Regeneration of the trap is accompaniedby a lowering of the resistance to flow of (exhaust) gas through thetrap; it is detected by a decrease in the pressure drop across the trap.

The term "fuel" includes any hydrocarbon that can be used to generatepower or heat. The term also covers fuel containing other additives suchas dyes, cetane improvers, rust inhibitors, antistatic agents, guminhibitors, metal deactivators, de-emulsifiers, upper cylinderlubricants, and anti-icing agents. Preferably, the term covers dieselfuel.

The term "diesel fuel" means a distillate hydrocarbon fuel or forcompression ignition internal combustion engines meeting the standardsset by BS 2869 Parts 1 and 2 as well as fuels in which hydrocarbonsconstitute a major component and alternative fuels such as rape seed oiland rape oil methyl ester.

The combustion of the fuel can occur in, for example, an engine such asa diesel engine, or any other suitable combustion system. Examples ofother suitable combustion systems include recirculation engine systems,domestic burners and industrial burners.

The term "species capable of acting as a Lewis base" includes any atomor molecule that has one or more available electron pairs in accordancewith the Lewis acid-base theory.

The term "induces acceptable spontaneous trap regeneration according tothe Test Protocol presented in the Examples" means that the compositionis of high effectiveness, when the composition is tested according tothe Test Protocol presented in the Examples (see later).

The present invention therefore relates to additives for liquidhydrocarbon fuels, and fuel compositions containing them. In particularthe invention relates to additives effective in reducing the levels ofparticulate and/or unburned hydrocarbon in the exhaust. Morespecifically the invention relates to additives effective to reduce theparticulate and/or unburned hydrocarbon content of exhaust gas emissionsfrom diesel engines. Furthermore the invention relates to fuel additivepreparations that lower the ignition temperature and enhance thecombustion of trapped particulate matter. Especially, the inventionrelates to fuel additive preparations that lower the ignitiontemperature and enhance the combustion of trapped particulate matterfrom diesel engines. The present invention therefore provides additivesfor fuel that give an overall reduction in the environmental damageresulting from the combustion of that fuel.

In addition to the advantages outlined above, it is to be noted thatwhen traps are used with the compositions of the present invention theneed for an external energy input for regeneration is greatly reduced orin some instances eliminated. Thus, the fuel additive of the presentinvention can be effective in reducing engine out emissions andespecially as a combustion catalyst aiding the oxidation of trappedparticles. The additive therefore provides for simpler, safer and lesscostly traps by enabling less frequent, less intense or less energeticregeneration, whether the heat required for regeneration is provided bythe exhaust gas or through some external mechanism.

In a preferred embodiment, the compositions of the present inventionyield water soluble products after the combustion thereof. In thisregard, there is an advantage because if the additive metals provideultimate products that are readily water soluble so recycle ofparticulate traps becomes simpler and less costly.

In a preferred embodiment the composition of the present invention isfuel-soluble or fuel miscible. With these aspects, the present inventionprovides concentrates of the composition (additive) in a solvent fullycompatible with fuels, especially diesel fuels, such that blending offuel and additive may be more easily and readily carried out. Thisserves to reduce the complexity and cost of any on-board dosing device.

In a preferred embodiment the composition (additive) of the presentinvention is at least resistant and preferably totally inert towardswater leaching. With this aspect, the present invention provides acomposition that is very compatibile with fuel handling, storage anddelivery thereof. In particular, diesel fuel often encounters water,especially during delivery to the point of sale, and so suchcompositions would be of enormous benefit for this type of fuel.

In one aspect of the present invention, the alkali metal and alkalineearth metal complexes of the present invention have the general formula

    M(R).sub.m.nL

where M is the cation of an alkali metal or an alkaline earth metal ofvalence m, R is the residue of an organic compound of formula RH where Hrepresents an active hydrogen atom reactive with the metal M andattached either to a hetero atom selected from O, S and N in the organicgroup R, or to a carbon atom, that hetero or carbon atom being situatedin the organic group R close to an electron withdrawing group, e.g. ahetero atom or group consisting of or containing O, S or N, or aromatic:ring, e.g. phenyl, n is a number indicating the number of organicelectron donor molecules (Lewis bases) forming dative bonds with themetal cation in the complex, usually up to five in number, more usuallyan integer from 1 to 4, and L is one or more organic electron donorligand (Lewis base). R may comprise one or more functional groupscapable of acting as an organic electron donor ligand.

In a more detailed aspect, the Lewis base metallo-organic co-ordinationcomplexes used in accordance with the present invention contain theresidue of an organic molecule RH which contains an active hydrogen atomH which is replaceable with a metal cation. In the organic compound RHthe active hydrogen atom will be attached to a hetero atom (O, S, or N)or to a carbon atom close to an electron withdrawing group. The electronwithdrawing group may be a hetero atom or group consisting of orcontaining O, S, or N, e.g. a carbonyl (>C═O), thione (>C═S) or imide(>C═NH) group, or an aromatic group, e.g. phenyl. When the electronwithdrawing group is a hetero atom or group, the hetero atom or groupmay be situated in either an aliphatic or alicyclic group, which, whenthe active hydrogen group is an NH group, may or may not, but usuallywill contain that group as part of a heterocyclic ring.

Suitable complexes are derived from a β-diketone of the formula

    R.sup.1 C(O)CH.sub.2 C(O)R.sup.2

where R¹ or R² is C₁ -C₅, alkyl or substituted alkyl, e.g. halo-,amino-, alkoxy- or hydroxyalkyl-, C₃ -C₆ cycloalkyl, benzyl, phenyl orC₁ -C₅ alkylphenyl, e.g. tolyl, xylyl, etc., and where R¹ may be thesame as or may be different to R².

Suitable β-diketones include: hexafluoroacetylacetone: CF₃ C(O)CH₂C(O)CF₃ (HFA); 2,2,6,6-tetramethylheptane-3,5-dione: (CH₃)₃ CC(O)CH₂C(O)C(CH₃)₃.

If the active hydrogen atom is attached to oxygen in the organiccompound RH, then suitable compounds include C₆₋₃₀ phenolic compounds,preferably substituted phenols containing from 1-3 substituents selectedfrom alkyl, alkylaminoalkyl, and C₁₋₈ alkoxy groups, e.g. cresols,guiacols, di-t-butylcresols, dimethylaminomethylenecresol. Thesubstituted phenols are particularly preferred. Especially preferredsuch metal complexes are those derived from reaction of a metalhydroxide or other alkali or alkaline earth metal source with an alkylor alkenyl substituted succinic anhydride or the hydrolysis product.Typically such anhydrides are those prepared by reaction of oligomerisedisobutenes with maleic anhydride. A wide variety of such materials and arange of techniques for their preparation are known to those skilled inthe art. In general, a high molecular weight poly(isobutene) substituentprovides the resulting complex with good hydrocarbon solubility at thecost of lower metal content. We have found the alkenyl substitutedsuccinic anhydride derived from the thermal reaction of BP Napvis X-10™with maleic anhydride to give a good compromise between hydrocarbonsolubility and metal content. It is considered that in such compoundsone carboxylic acid group is deprotonated and bound in salt-like fashionto metal ion and the second carboxylic acid group is protonated andbound to metal ion as a Lewis base.

If the active hydrogen is attached to a nitrogen atom in the organiccompound RH, then suitable compounds are heterocyclic compounds of up to20 carbon atoms containing a --C(Y)--NH-- group as part of theheterocycle, Y being either O, S or ═NH. Suitable compounds aresuccinimide, 2-mercaptobenzoxazole, 2-mercapto-pyrimidine,2-mercaptothiazoline, 2-mercaptobenzimidazole, 2-oxobenzoxazole.

In more detail, L can be any suitable organic electron donor molecule(Lewis base), the preferred ones being hexamethylphosphoramide (HMPA),tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine,dimethylpropyleneurea (DMPU), dimethylimidazolidinone (DMI),dimethylcarbonate (DMC), dimethylsulphoxide (DMSO), dimethylformamide(DMF). Other possible ligands are diethylether (Et₂ O),1,2-dimethoxyethane (monoglyme), bis(2-methoxyethyl)ether (diglyme),dioxane, tetrahydrofuran. Where R comprises L, L is conveniently afunctional group capable of acting as a Lewis base donor, preferred onesbeing dimethylaminomethyl (--CH₂ N(CH₃)₂), ethyleneoxy (--OCH₂ CH₂ O--),ethyleneamine (--N(R)CH₂ CH₂ N(R)--), carboxyl(--CO₂ H) and ester(--CO₂CH₂ --). It is to be understood that these listings are by no meansexhaustive and other suitable organic donor ligands or functional groups(Lewis bases) may be used.

The metal complex will usually contain 1-4 ligand molecules to ensureoil solubility, i.e. the value of n will usually be 1, 2, 3, or 4. WhereR comprises L, n can be and often is zero.

The Lewis base metallo-organic salt complexes used in the invention canbe obtained by reacting a source of the metal M, e.g. the elementalmetal, a metal alkyl or hydride, an oxide or a hydroxide, with theorganic compound RH in a hydrocarbon, preferably an aromatic hydrocarbonsolvent such as toluene, containing the ligand in a stoichiometricamount or in an excess amount.

Whilst any of the alkali (Group I: Atomic Nos. 3, 11, 19, 37, 55) andalkaline earth (Group II: Atomic Nos. 4, 12, 20, 38, 56) may be used asthe metal (or metals) M, preferred are the donor ligand complexes ofsodium, potassium, strontium or calcium. The metal hydroxide willtypically be the preferred source of the metal, on economic grounds.

Whilst the organometallic compounds described may be added directly tothe fuel, either external to the vehicle or by using an on board dosingsystem, they will preferably first be formulated as a fuel additivecomposition or concentrate containing the substance, or mixtures thereofpossibly along with other additives, such as detergents, anti foams,dyes, cetane improvers, corrosion inhibitors, gum inhibitors, metaldeactivators, de-emulsifiers, upper cylinder lubricants, anti-icingagents, etc., in an organic carrier miscible with the fuel.

Without wishing to be bound by theory it is believed that thecompositions of the present invention are effective in view of theirlower molecular weight and/or lower molecular size than the morecommonly used overbased materials which are micellar in nature. In thisregard, it is believed that a more `molecular` species will be moreevenly distributed throughout the fuel and so show greater efficiency.In addition, it is believed that charge transfer type mechanisms mayplay a part. In this regard, the metal may act as charge transfer agent,causing soot particles to acquire charge. The tendency of like chargesto repel then reduces agglomeration of soot particles. Thus changes inmorphology would be responsible for ready oxidation of the particle. Inaddition is is believed that the generation of hydroxyl radicals are toplay a part. In this regard, the metals (group 2 in particular) maycatalyse the generation of OH radicals which are known to be importantin flame propagation in fuel rich flames.

In addition, it is believed that the formation of combustion initiatorsmay play a part. In this regard, the metal may form a peroxide (sodiumis known to do this on combustion in air) which is particularly reactivetowards carbonaceous soot and so initiates reaction at lowertemperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

The test protocol that follows employed an exhaust gas filter or trapshown in the attached drawings in which:

FIG. 1 is a cross sectional view of an exhaust gas filter trapcontaining radial flow filter cartridges used in parallel;

FIG. 2 is a perspective view of a radial flow filter cartridge of FIG. 1partially broken away showing a collandered steel tube spiral wound withfiber; and

FIG. 3 is a longitudinal and cross-sectional view of the radial flowfilter cartridge of FIG. 2.

The present invention will now be described only by way of the followingnon-limiting examples.

In the following Examples reference shall be made to a Test Protocolwhich is outlined later on. This Test Protocol provides an easy means todetermine if a fuel additive would be acceptable as a compositionaccording to the present invention. A composition is acceptable if thecomposition is of high effectiveness when the composition is testedaccording to this Test Protocol. It is to be noted that the claims arenot limited to the compositions when only used in this Test Protocol.

TEST PROTOCOL

The tests were carried out in a Renault truck on a rolling roaddynamometer, detailed specifications are given below.

MAKE: Renault 50 Series S35 truck

FIRST REGISTERED: 14th August 1990

UNLADEN WEIGHT: 2483 kg

MAX. LADEN WEIGHT: 3500 kg

ENGINE: PERKINS PHASER 90, normally aspirated, 4 Cylinder in line watercooled, 16.5:1 Compression ratio

ENGINE CAPACITY: 3990 cm³

RATED POWER: 62 kW at 2800 rpm

BORE: 100 mm

STROKE: 127 mm

FUEL PUMP: Bosch type EPVE direct injection design

TRANSMISSION: Rear wheel drive

The vehicle was additionally equipped with an exhaust gas filter ortrap. The filter trap comprised radial flow filter cartridges XW3C-053(from 3M Corporation) employed in parallel--as shown in FIG. 1. Thecartridges were arranged at the corners of an equilateral triangle--asshown in FIG. 1. Nextel (Trade mark of 3M Corporation) fibre is suppliedwound in spiral fashion about a collandered 50×4 cm steel tube--as shownin FIGS. 2 and 3. The cartridges were used as supplied. The distancefrom the engine manifold to the entrance to the trap was about onemeter. The exhaust pipe and trap were lagged with insulating material.

Additised fuel was prepared by dissolving the required amounts ofadditive in one liter of base diesel fuel, then diluting in the basefuel until the fuel finally contained an additional 5 ppm m/m of themetal above background level. Base fuel used was BPD26, as specifiedbelow.

    ______________________________________                                        DIESEL ANALYSIS                                                               ______________________________________                                        DESCRIPTION OF SAMPLE                                                                             BPD26                                                     SAMPLE NO.          944929                                                    DENSITY @ 15° C.                                                                           0.8415                                                    VISCOSITY @ 20° C.                                                     VISCOSITY @ 40° C.                                                                         3.060                                                     CLOUD POINT ° C.                                                                           -5                                                        CFPP ° C.    -14                                                       POUR POINT ° C.                                                                            -15                                                       FLASH POINT ° C.                                                                           70.5                                                      SULPHUR % WT.       0.13                                                      Initial boiling point @ ° C.                                                               185.5                                                     5% VOL. @ ° C.                                                                             209.8                                                     10% VOL. @ ° C.                                                                            224                                                       20% VOL. @ ° C.                                                                            246.1                                                     30% VOL. @ ° C.                                                                            260.8                                                     40% VOL. @ ° C.                                                                            271.5                                                     50% VOL. @ ° C.                                                                            280.6                                                     65% VOL. @ ° C.                                                                            294.8                                                     70% VOL. @ ° C.                                                                            299.6                                                     85% VOL. @ ° C.                                                                            319.8                                                     90% VOL. @ ° C.                                                                            330.1                                                     95% VOL. @ ° C.                                                                            347.0                                                     FBP @ ° C.   360.4                                                     % VOL. RECOVERY     98.1                                                      % VOL. RESIDUE      1.8                                                       % VOL. LOSS         0.1                                                       C.C.I. (IP41)       54.5                                                      C.C.I. (IP380)      53.2                                                      CETANE IMPROVER - % NIL                                                       CETANE NUMBER       54.2                                                      ______________________________________                                    

The test was in two parts; A soot collection or trap blocking phase, andA forced filter regeneration or burn off stage.

The soot collection phase consisted of running the truck at steady speedand level road drag power for the unladen vehicle such that for a cleantrap the exhaust gas temperature was about 195° C. at the inlet to thetrap. This driving condition was continued until the soot loading causedthe pressure drop across the filter to reach a value of 200 mbar (150mbar was used during some early runs).

The forced filter regeneration stage entailed increasing the exhaust gastemperature until the soot collected on the trap ignited and burnt off.This was achieved by increasing vehicle speed to about 90 km/hr anddynamometer load towards 300 Nm at 5 Nm/min. This was done at theconclusion of each sooting phase i.e. when the pressure drop reached 200mbar.

Ignition of the soot was inferred by observing a decrease of pressuredrop across the filter. `Forced` ignition occurred at exhaust gastemperatures of >300° C. `Spontaneous` burnoff or ignition is that whichocurs at or below about 200° C.

Each sequence of runs using a given additised fuel was preceded by aminimum of three sequences of trap blocking and soot burn off orregeneration, as described above. For this base untreated fuel was used.Typically, the exhaust gas temperature range 500 to 550° C. werereached. The time to load the trap decreased with successive runs usingbase fuel (reference fuel data).

Runs using additised fuel were characterised in that spontaneous sootignition and prolonged soot collection phases to reach the `blocked`condition were observed. The degree to which these phenomena wereobserved varied between one additised fuel and another.

Additives were characterised as follows.

1. An additive was considered to be of "high effectiveness" if two orfewer sequences of filter sooting and regeneration were required beforea period of prolonged soot collection running, i.e. greater than 12hours, was achieved without the need for a forced regeneration;typically ten or more spontaneous soot ignitions were observed when thiswas achieved.

2. An additive was considered to be of "low effectiveness" if the aboveconditions regarding prolonged soot collection running and/or number offorced regenerations required were not met, but nevertheless somespontaneous ignitions were observed.

3. An additive was considered "ineffective" if after five sequences ofsoot collection running and forced burnoff no episodes of spontaneousignition or prolonged running, i.e. greater than six hours, had beenobserved.

EXAMPLE 1 Preparation of 1,3-dimethylimidazolidinone Adduct of Sodium2,2,6,6-tetramethylheptane-3,5-dionate: [Na(TMHD).DMI]

A round bottom flask was charged under nitrogen with sodium hydride(NaH, 4.8 g, 200 mmol), dry toluene (100 cm³) anddimethylimidazolidinone (23.8 cm³, 22.8 g, 200 mmol).2,2,6,6-tetramethylheptane-3,5-dione (HTMHD, 43 cm³, 37.97 g, 206 mmol)was then added dropwise by syringe against nitrogen flush. After theaddition of a few drops an effervesence was noted. The solution wasstirred and gently warmed (oil bath, 60° C.) during one hour beforefiltration. A 90% plus yield of NaTMHD.DMI crystals grew onrefrigeration.

Melting point 70-72° C., C/H/N found versus (calculated) wt %, C 60.09(60.00), H 9.14 (9.06) and N 8.67 (8.85), ¹ H nmr in C₆ D₆ shifts rel.to TMS 5.873 ppm (s, H, COCHCO), 2.609 (s, 6H, NCH₃), 2.570 (s, 4H, CH₂CH₂) and 1.396 (s, 18H, C(CH₃) ₃).

EXAMPLE 2 Preparation of Sodium Salt of Poly(isobutenyl) Succinic Acid,Approx. 1,000 Molecular Weight [Na(PIBSA₁₀₀₀)]

A suspension of powdered solid sodium hydroxide (8.04 g, 200 mmol) in asolution of poly(isobutenyl) succinic anhydride (PIBSA, 198.8 g, 200mmol) in dry toluene (995 cm³) was allowed to stir at ambienttemperature during several days. The solids dissolved to yield a clearsolution of 1000 molecular weight poly(isobutenyl)succinic acid,monosodium salt.

EXAMPLE 3 Preparation of Dimethylcarbonate Adduct of the Sodium Salt of2,6-ditertiarybutyl-4-methyl Phenol: [(NaBHT)₂.3DMC]

A solution of 2,6-ditertiarybutyl-4-methyl phenol (butylated hydroxytoluene, BHT, 21.8 g, 100 mmol) in dry toluene 100 cm³) is added to asuspension of sodium hydride (2.4 g, 100 mmol) in dry toluene (100 cm³)and dimethyl carbonate (12.64 cm³, 13.51 g, 1.5 equiv) under inertatmosphere. Precipitation of white material accompanied the evolution ofhydrogen gas and heat. After completion of the addition the reactionmixture was stirred at ambient temperature during some 60 minutes. Thesolids were isolated by fitration and dried under vacuum.

C/H/N found versus (calculated) wt %, C 62.40 (62.07) and H 8.28 (8.49).

EXAMPLE 4 Preparation of the Dimethylimidazolidinone Adduct of theStrontium Salt of 2,2,6,6-tetramethylheptane-3,5-dione;[Sr(TMHD)₂.3DMI]

HTMHD (21 cm³, 18.54 g, 100.6 mmol) was added under inert atmosphere toa solution of dimethylimidazolidinone (30 cm³, 32.32 g, 283 mmol) in drytoluene (20 cm³) containing a piece (6 g) of strontium metal. Animmediate effervesence was noted. The contents of the flask were stirredand warmed (80° C., oil bath) overnight yielding a yellowy solution andsome colourless solids. The solids were dissolved by the addition offurther toluene (30 cm³) and unreacted Sr removed by filtration.Refrigeration yielded large block-shaped crystals of [Sr(TMHD)₂.3DMI] in90% yield.

EXAMPLE 5 Preparation of the Stontium Salt of Molecular Weight 1,000Poly(isobutenyl) Succinic Anhydride [Sr (PIBSA₁₀₀₀)₂ ]

Poly (isobutenyl) succinic anhydride, 1,000 molecular weight, (69.48 g,69 mmol) was weighed into a round-bottom flask. Dry toluene (347 cm³)was added. The mixture was heated and stirred to form a homogenoussolution. Strontium hydroxide octahydrate (6.90 g 26 mmol) was thenadded cautiously. Some frothing accompanied the addition. The mixturewas refluxed during one hour then left to stir overnight. A Dean-Starkaparatus was then used to remove 3.8 cm³ of water. The resultingslightly turbid solution was filtered, 0.7 g of solids were recovered. Afinal solution concentration of 0.56 wt % Sr as Sr(PIBSA₁₀₀₀)₂ wasachieved.

EXAMPLE 6 Preparation of Dimethylimidazolidinone Adduct of Calcium Bis2,2,6,6-tetramethylheptane-3,5-dionate, [Ca(TMHD)₂.2DMI].

Calcium hydride (0.42 g, 10 mmol) suspension in toluene (20 cm³) in thepresence of two equivalents of dimethylimidazolidinone (2.2 cm³, 20mmol) is allowed to react with four equivalents of2,2,6,6-tetramethylheptane-3,5-dione (40 mmol, 8.4 cm³). After theinitial exotherm dies down the mixture is stirred and gently warmed toyield a clear solution. The solution is filtered, reduced in volumeuntil crystals begin to appear, then heated to redissolve the crystals.Recrystallisation is then found on refrigeration.

EXAMPLE 7 Preparation of the 1,3-dimethylimidazolidinone (DMI) Adduct ofPotassium 2,2,6,6-tetramethyl-3,5-heptanedionate: [{K(TMHD)}₂.DMI]

Potassium hydride (KH, 0.90 g, 22.5 mmol) was washed of mineral oil,dried and placed in a Schlenk tube. Hexane was then added followed byDMI (7 ml, 64.22 mmol). Some effervescence occurred, implying reactionor dissolution, and a green coloration was apparent. TMHD (4.4 ml, 21.05mmol) was then added slowly, as a very vigorous reaction takes place.After about fifteen minutes the reaction subsided and an oil settled outof solution. The two-phase liquid was cooled in an ice-box (to -10° C.)and a solid crystalline mass formed from the oil part over about half anhour.

The crystalline solids were washed with hexane, isolated and determinedto be a dimethylimidizolidinone adduct of potassium2,2,6,6-tetramethylheptane-3,5-dione: [{K(TMHD)}₂.DMI] Yield 1.7 g, 16%first batch based on a 1:2 ligand:donor ratio

Formula: K[(CH₃)₃ C(--O)CH₂ C(═O)C(CH₃)₃ ].O═CN(CH₃)CH₂ CH₂ N(CH₃) , Mw450.678 m.p. 64-68° C.

EXAMPLE 8 Dimethylimidazolidinone Adduct of Potassium2,6-ditertiarybutyl-4-methyl Phenol, [K(BHT).2DMI]

The method of example 4 is used, with the appropriate change in Lewisbase:metal ratio. The adduct is sufficiently soluble in toluene topermit recrystallisation. The microcrystals obtained have melting point92-96° C.

EXAMPLE 9 Dimethylimidazolidinone Adduct of Sodium2,6-ditertiarybutyl-4-methyl Phenol, [Na(BHT).3DMI]

The method of example 4 is used, with the appropriate change in Lewisbase:metal ratio. The adduct is sufficiently soluble in toluene topermit recrystallisation. The crystals obtained have melting point96-98° C.

EXAMPLE 10 Dimethylimidazolidinone Adduct of Sodium 2-methoxy Phenol,[Na(TMP).DMI]

The method of example 4 is used, with the appropriate change in Lewisbase:metal ratio. The adduct is sufficiently soluble in toluene topermit recrystallisation. The crystals obtained have melting point87-89° C.

EXAMPLE 11 Dimethylimidazolidinone Adduct of Strontium Bis2,4,6-trimethylphenol, [{Sr(TMP)₂ }₂.5DMI]

The method of example 4 is used, with the appropriate change in Lewisbase and phenol:metal ratio. The adduct is sufficiently soluble intoluene to permit recrystallisation. The fine needle-like crystalsobtained have melting point 244° C.

EXAMPLE 12 Preparation of the Sodium Salt of Molecular Weight 420Poly(isobutenyl)succinic Anhydride

A thermostatted `Soverel`™ reactor was charged with BP Hyvis XD-35™poly(isobutene) (665.79 g, no. av. mol. wt. 320, 2.08 mol) and maleicanhydride (411.79 g, 4.2 mol, 2.02 equivalents). The contents wereheated to 200° C. with oil circulated through the jacket by an externaloil bath and strongly stirred during 8 hours. A viscous, dark brownsolution formed. The unreacted maleic anhydride was removed undervacuum, along with some of the unreacted poly(isobutene). A materialanalysing at 11.2 wt % poly(isobutene) was recovered.

A sample of the material prepared above (535.78 g, theoretical 1.125moles PIBSA₄₂₀) was charged to a flat-bottomed glass vessel fitted withturbine agitator, thermocouple well and charging port. The vessel wasfurther charged with Solvesso 150™ (502.26 g). The contents were warmedto 82° C. via an external oil bath and stirred until homogenous. Beadedsodium hydroxide (46.03 g, 1.15 moles) was then charged. The resultingsuspension of white 1 mm beads in brown solution was stirred overnightat 78° C. Material (1066.19 g) containing 2.13 wt % sodium as 420molecular weight poly(isobutenyl)succinic acid, monosodium salt, wasobtained.

EXAMPLE 13 Preparation of No. Average Molecular Weight 420Poly(isobutylene) Succinic Anhydride-PIBSA₄₂₀

A reactor was charged with BP-Hyvis XD-35™ poly(isobutylene) (12.906 kg,40.33 mol) and heated to 100° C. with stirring before adding maleicanhydride (5.966 kg, 60.88 mol). The temperature of the oil bathsupplying the reactor jacket was set to 220° C., the internal reactortemperature reached 185° C. after three hours. This was taken as thestart of the reaction time. The oil bath temperature was lowered to 212°C. and the reaction mix stirred during some 30 hours. At the end of thisperiod a vacuum was applied and the excess amleic anhydride distilledout. After 15 hours under vacuum, residual maleic anhydride content was0.0194 wt % and residual PIB 19.9 wt %. Some 13.888 kg of brown, viscousmaterial was recovered.

EXAMPLE 14 Preparation of Strontium Salt of PIBSA₄₂₀

A reactor was charged with material prepared in Example 13 (555.81 g,445.99 g, 1.06 mol PIBSA₄₂₀, 109.82 g, 343 mmol PIB₃₂₀) and Solvesso150™ (346.46 g). This mixture was stirred and heated until homogenous.Strontium hydroxide octahydrate (140.43 g, 0.53 mol) was then added andheated to 50° C. overnight. Water (40.62 g), was removed by heating thesolution to 120° C. Product contained 5.36 wt % Sr as Sr(PIBSA₄₂₀)₂.

EXAMPLE 15 Preparation of Potassium Salt of PIBSA₄₂₀

An oil-jacketed reactor was charged with material prepared in Example 13(440.78 g, 0.85 mol PIBSA420), and Solvesso 150™ (462.53 g). Thecontents were warmed to 50° C. and stirred until homogenous. KOH flake(47.88 g, 0.77 mol if 10% H₂ O) was then added with stirring and theresulting suspension left to stir overnight. The solids dissolved andFTIR analysis showed an absence of the 1863 cm⁻¹ absorption due to thePIBSA. The solution contained 3.33 wt % K as K(PIBSA₄₂₀).

EXAMPLE 16 Preparation of No. Average Molecular Weight 360Poly(isobutylene) Succinic Anhydride (PIBSA₃₆₀)

A number average molecular weight 260 poly(isobutylene) (PIB₂₆₀,BP-Napvis X10™, 586.2 g, 2.257 moles) was charged to a one literoil-jacketed reaction vessel. The vessel was further charged with maleicanhydride (442.71 g, 4.52 moles). The mixture was heated to 200° C. andstirred during 24 hours. At the end of this period, the maleic anhydridewas removed by vacuum distillation.

A dark brown, viscous oil was recovered, this analysed as PIBSA₃₆₀containing 8.1% m/m PIB₂₆₀.

EXAMPLE 17 Preparation of Sodium Salt of No. Average Molecular Weight360 Poly(isobutylene) Succinic Acid-Na(PIBSA₃₆₀)

A reactor was charged with a sample of poly(isobutylene)succinicanhydride prepared as above (412.91 g, 392.26 g PIBSA360, 1.096 moles,20.65 g PIB260). The vessel was further charged with Solvesso 150™(526.19 g) and the liquids heated and stirred to form a homogenous deepbrown solution. Sodium hydroxide as dry pellets (43.84 g, 1.096 mol) wasthen added. The resulting suspension was stirred overnight at 70° C.FTIR indicated complete consumtion of the PIBSA and formation ofcarboxylic acid and carboxylic acid salt. The solution was decanted andanalysed as containing 2.35 wt % Na as Na(PIBSA₃₆₀).

EXAMPLE 18 Preparation of Strontium Salt of No. Average Molecular Weight360 Poly(isobutylene) Succinic Acid-Sr(PIBSA₃₆₀)₂

A jacketed reactor was charged with poly(isobutylene) succinincanhydride prepared as in Example 16 (468.43 g, 451.10 g, 1.26 molesPIBSA, 37.33 g PIB) and Solvesso 150™ (568.90 g), the two were heated to50° C. and stirred to yield a homogeneous solution. Sr(OH)₂.8H₂ O(170.79 g, 0.64 mol) was then added. The resulting suspension was thenstirred until the solids had dissolved. No attempt was made to separatethe water.

Comparative Example 1: Preparation of Sodium Salt of Tertiary AmylAlcohol, [NaOtAm], as a 20 wt % Solution in Xylene

Sodium stored under mineral oil was cleaned of the outer layer ofoxide/hydroxide then cut into 1 cm cubes under toluene. The pieces wereshaken dry in air, then charged (50.27 g) to a tared electrically heatedvessel equipped with nitrogen flush and carrot valve. The sodium wasmelted out then added via the valve and under inert atmosphere to around bottom flask containing dry mixed xylenes (400 g, 465 cm³) 38.45 g(1.67 moles) was found to have been so transferred. Further dry mixedxylenes (175 cm³, 152 g) were then added to the reaction flask. Theheated vessel was then replaced with a reflux condenser. The reactionflask was additionally fitted with a pressure equalising droppingfunnel. The flask was heated in an oil bath until the sodium becamemolten. Rapid stirring yielded a silvery suspension. The dropping funnelwas charged with tertiary amyl alcohol (182 cm³, 155 g). The alcohol wasadded with caution over about thirty minutes. A moderate evolution ofhydrogen was noted. The reaction was heated with stirring during some 18hours during which time a clear, colourless solution resulted. Thesolution was tranferred through a cannula to dry bottles which were thenfirmly sealed against ingress of oxygen or moisture.

Comparative Example 2: Preparation of Sodium Dodecylbenzene SulphonateOverbased Eight Times with Sodium Carbonate

A stable dispersion in mineral oil of overbased sulphonic acid wasprepared as described in GB 1481553, save that poly(isobutenyl)succinicanhydride of average molecular weight 1000 (142 g) versus 560 (71 g) wasused.

Comparative Example 3: Sodium Tert-butoxide in Propan-2-ol

All aparatus was dried in an oven at 120° C. and cooled either under aflow of nitrogen or during admission to the dry box. A round-bottomflask was charged in the dry box with sodium tert-butoxide powder(20.126 g, Aldrich, fresh bottle). The flask was stoppered and removedfrom the dry box and fitted with nitrogen flush, overhead stirrer andpressure-equalised dropping funnel. The dropping funnel was then chargedwith anhydrous propan-2-ol (820.94 g, Aldrich) by cannula from the`Sure-Seal`™ bottle. The alcohol was added slowly with stirring andgentle warming to the alkoxide. A pale green, clear solution resulted.

Engine out Emissions Reduction

The engine used for the testing was a single cylinder version of thePerkins 4-236 normally aspirated direct injection engine. This engine iselsewhere referred to as a Perkins 236-S engine. The engine was arrangedso that only the cylinder nearest the flywheel was operative. The fuelpump was a Simms plunger unit to be operating to supply the firingcylinder. The fuel system was arranged to allow easy changing of fuel,without contamination from one fuel to another. Fuel was blended bystandard methods to contain 10 ppm m/m of additive metal.

The engine was connected to drive a Heenan & Froude eddy currentdynamometer controlled by a test bed control system. The speed of theengine and dynamometer could be measured by a magnetic pick up and a 60toothed wheel arrangement. A load cell was arranged to indicate thetorque absorbed by the dynamometer.

The inlet air to the engine was conditioned by a special purpose unit todehumidify and ensure the air supply was held at constant temperature.

The test bed was equipped with a computer based data logging system.

Smoke measurement was carried out by a Celesco model 107 obscurationtype smoke meter having a 100 mm light path. A Bosch smoke meter drawingone liter of exhaust gas through a standard filter paper was also used.A Bosch envigilator unit was used to grade the filter paper blackening.

Unburnt hydrocarbons were determined by sampling exhaust gas through aheated line to a Beckman Flame Ionisation Detector (FID model 402).Hydrocarbons were measured in terms of carbon one equivalent.

Base fuel used was BPD25 as described below.

    ______________________________________                                        DIESEL ANALYSIS                                                               ______________________________________                                        DESCRIPTION OF SAMPLE                                                                             BPD25                                                     SAMPLE NO.          933117                                                    DENSITY @ 15° C.                                                                           0.8373                                                    VISCOSITY @ 20° C.                                                     VISCOSITY @ 40° C.                                                                         2.988                                                     CLOUD POINT ° C.                                                                           -3                                                        CFPP ° C.    -17                                                       POUR POINT ° C.                                                                            -21                                                       FLASH POINT ° C.                                                                           67                                                        SULPHUR % WT.       0.17                                                      FIA: - % VOL. SATURATES                                                                           73.2                                                      % VOL. OLEFINS      1.3                                                       % VOL. AROMATICS    25.5                                                                          177.3                                                     5% VOL. @ ° C.                                                                             199.9                                                     10% VOL. @ ° C.                                                                            212.9                                                     20% VOL. @ ° C.                                                                            237.2                                                     30% VOL. @ ° C.                                                                            255.1                                                     40% VOL. @ ° C.                                                                            268.8                                                     50% VOL. @ ° C.                                                                            279.8                                                     65% VOL. @ ° C.                                                                            295.6                                                     70% VOL. @ ° C.                                                                            301.1                                                     85% VOL. @ ° C.                                                                            324.2                                                     90% VOL. @ ° C.                                                                            334.5                                                     95% VOL. @ ° C.                                                                            350.7                                                     FBP @ ° C.   363.9                                                     % VOL. RECOVERY     98.6                                                      % VOL. RESIDUE      1.4                                                       % VOL. LOSS         0.0                                                       C.C.I. (IP 218)                                                               C.C.I. (IP 364)     53.9                                                      CETANE IMPROVER - TYPE                                                        CETANE IMPROVER - % NIL                                                       CETANE NUMBER       52.3                                                      ______________________________________                                    

The following data were obtained at engine speed 1350 rpm, load 55 Nm.

    ______________________________________                                                      Reduction over base, untreated fuel (%)                                       Smoke and hydrocarbon emissions                                 Additive   Example  Bosch     Celesco HC                                      ______________________________________                                        NaTMHD.DMI 1        5.3       11.8    14.2                                    NaTMHD.DMI 1        10.2      13.7    28.6                                    mean                7.8       12.8    21.4                                    Sr(TMHD).sub.2.3DMI                                                                      4        3.4       9.3     6.2                                     Sr(TMHD).sub.2.3DMI                                                                      4        8.6       7.1     10.1                                    Sr(TMHD).sub.2.3DMI                                                                      4        6.7       7.6     5.6                                     mean                6.2       8.0     7.3                                     Ca(TMHD).sub.2.2DMI                                                                      6        2.0       5.3     -3.4                                    K(TMHD).0.5DMI                                                                           7        2.7       17.9    25.0                                    K(BHT).2DMI                                                                              8        10.4      3.7     12.2                                    ______________________________________                                    

The following data were obtained on the same set up, at an engine speedof 1350 rpm, varying the load on the dynamometer as described in thetable.

    __________________________________________________________________________              Reduction over base, untreated fuel (%)                                       Bosch smoke                                                         Compound/(Example)                                                                      10 Nm                                                                              20 Nm                                                                             30 Nm                                                                              40 Nm                                                                             50 Nm                                                                              Max. torque                                  __________________________________________________________________________    Na(TMHD).DMI(1)                                                                         23   33  30   37  -1   -13                                          Sr(TMHD).sub.2.3DMI(4)                                                                  58    0  11   35    0  1                                            K(TMHD).0.5DMI(7)                                                                       48   39  31   15    8  7                                            K(TMHD).0.5DMI(7)                                                                       43   33  36   -9  -1   8                                            K(BHT).2DMI(8)                                                                          26   29  20    2    4  6                                            Na(TMP).DMI(10)                                                                         46   16  44   22  -5   -6                                           __________________________________________________________________________

Static Engine Smoke Reduction Tests

Examples of metal PIBSAs, all prepared from PIBSA obtained as in Example13 from maleinisation of BP Hyvis XD-35™, were added to a commercialdiesel fuel conforming to BS 2869 to provide metal concentrations of 10mg/kg of fuel and tested in a static Perkins 236-S DI single cylinderresearch engine. The blend data were as follows:

    ______________________________________                                              Prepared by                                                                             Metal   Compound                                                                              method Metal mg/l                             Metal method of atomic  mg/kg fuel                                                                            mg/kg fuel                                                                           fuel                                   ______________________________________                                        Sr    Example 14                                                                              87.62   294.0   10     8.5                                    Na    Example 12                                                                              22.99   502.5   10     8.5                                    K     Example 13                                                                              39.10   293.0   10     8.5                                    ______________________________________                                    

The engine was run at a constant speed of 1400 rev/min at a brake loadof 55 Nm. The engine was run on base fuel (non additised), then changedto run on additsed fuel, then returned to running on base fuel, thenadditised fuel and so on throughout the testing period. Smoke emissionswere measured using an AVL 415 Smoke Meter. In this method a volume ofgas is drawn through a filter paper and the Filter Smoke Number (FSN) isobtained optically as a funtion of reduced reflectance. A large numberof measurements were taken for each fuel, the FSN reduction was definedas the difference between the average FSN on the additised fuel and theaverage FSN on the adjacent base fuel test (as a percentage of the basefuel test FSN). A series of such tests was conducted with each additiveand the average reduction is shown in the table below;

    ______________________________________                                                   Prepared by                                                        Metal      method of % reduction of FSN                                       ______________________________________                                        Sr         Example 14                                                                              12.3                                                     Na         Example 12                                                                              7.1                                                      K          Example 13                                                                              10.3                                                     ______________________________________                                    

The above data show the additives of the invention to be effective atreducing engine out emissions from a diesel engine.

Engine Tests

The compounds and compositions of the above-mentioned Examples weretested according to the Test Protocol mentioned above.

Compounds tested in chronological order were:

[Na(PIBSA₁₀₀₀)] (Example 2),

[Na tert amylate] (Comparative Example 1),

[{Na(BHT)}₂.3DMC] (Example 3),

[Sr(PIBSA₁₀₀₀)₂ ] (Example 5),

[Sr(TMHD)₂.3DMI] (Example 4),

[Na(TMHD).DMI] (Example 1),

Over based sodium dodecylbenzene sulphonate (Comparative Example 2), and

NaOtBu in propan-2-ol, (as described in DE-A-4041127) (ComparativeExample 3).

During the testing period the total distance accumulated was in excessof 30,000 km. As testing progressed the sooting time with base fuelincreased, i.e. it became more difficult to eliminate the memory ofadditised fuels. A typical soot collection running sequence on base fuelwas 5.14, 2.78, 2.18, 1.42 and 0.80 hours.

Results

For sodium tertiary amylate (Comparative Example 1) the soot collectionrunning times to achieve 200 mBar were: 0.72, 2.10, 1.80, 9.68 and 4.52hours. According to the protocol, the additive is regarded as of loweffectiveness.

The overbased sodium dodecylbenzene sulphonate (Comparative Example 2)required two sequences of sooting and burn off, after which it ran forsome 12 hours. Performance was marginal; on two occasions the exhaustpressure reached 200 mBar. The additive is of low effectiveness.

For sodium butyrate in iso-propanol (Comparative Example 3) the sootcollection running times to achieve 200 mBar were: 2.85, 2.61, 2.46,6.34, 2.53, and 2.22 hours. According to the protocol, this additive isalso classified as ineffective.

All other compounds tested were highly effective in preventing filterblocking, according to the test protocol.

Additives are here ranked according to the mean pressure drop across thetrap. Low pressure drop reflects ability to maintain trap cleanliness.

    __________________________________________________________________________    Rank               Fuel Bat.                                                                          Run Time                                                                           No. forced                                                                         Mean trap                                   Order                                                                            Example                                                                            Compound   No.  (hour)                                                                             regens.                                                                            (mBar)                                      __________________________________________________________________________    1  3    {Na(BHT)}.sub.2.3DMC                                                                     950790                                                                             18.00                                                                              1     65                                         2  1    Na(TMHD).DMI                                                                             951398                                                                             24.00                                                                              1     79                                         3  2    Na PIBSA   950705                                                                             17.75                                                                              1     80                                         4  C3   Overbase Na sulphonate                                                                   951811                                                                             12.00                                                                              2    104                                         5  4    Sr(TMHD).sub.2 3DMI                                                                      951326                                                                             20.24                                                                              2    116                                         6  5    Sr(PIBSA).sub.2 12.56                                                                              1    117                                         __________________________________________________________________________

Trap Regeneration Tests Using Cracked Wall Trap

A Peugeot 309 diesel, specified as below, was run in the mannerdescribed in the Test Protocol, save that no base fuel was used and the`Nextel™` fibre trap was replaced by a `cracked wall` trap prepared fromCorning EX80™. Higher dose rates of metal were found to be required inorder to obtain `spontaneous` regeneration of the trap (i.e regenerationwithout the need to increase engine speed and load). Sodium was blendedinto the fuel as the salt prepared by the method of Example 17. Resultsare presented in the form of peak back pressure and correspondingexhaust gas temperature at the trap inlet at onset of spontaneous trapregeneration.

    ______________________________________                                        Model             309 D                                                       Body              4 seat saloon                                               Arrangement       Front wheel drive                                           Kerb Weight kg    990                                                         Engine type       Diesel indirect injection                                   Swept volume 1    1.905, normally aspirated                                   Compression ratio 23.5:1                                                      Bore, stroke mm   83, 88                                                      Fuel pump         Rotary type Rotodiesel                                      Transmission      5 speed manual                                              ______________________________________                                    

    ______________________________________                                        Test No.                                                                              Sodium level ppm                                                                           Temp ° C.                                                                        Back pressure mBar                             ______________________________________                                        960663  25           <200      <200                                           960729  17           <210      <200                                           ______________________________________                                    

Acceptable temperature and pressure for spontaneous regeneration lieswithin the design and operation philosophy of the trap/enginecombination, in particular the fuel consumption penalty, due to the backpressure, that is deemed acceptable.

Other modifications will be apparent to those skilled in the art withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A method of regenerating a particulate filtertrap, said method comprising the steps of:(a) adding to a fuel beforethe combustion thereof a composition comprising as the soleorgano-metallic complex an organo-metallic complex of a Group I or aGroup II metal, wherein the concentration of the metal of theorgano-metallic complex in the fuel before combustion is 100 ppm orless, and wherein the organo-metallic complex comprises a Group I orGroup II metal salt of an alkyl or alkenyl-substituted succinic acid,and thereafter (b) combusting the fuel and passing the combusted gasesthrough a particulate filter trap to collect particles produced duringcombustion.
 2. The method as claimed in claim 1 wherein theconcentration of the metal of the organo-metallic complex in the fuelbefore combustion is 30 ppm or less.
 3. The method according to claim 1wherein the filter trap is a ceramic monolith trap and the concentrationof the metal of the organo-metallic complex in the fuel beforecombustion is 30 ppm or less .
 4. The method according to claim 1wherein the filter trap is a deep bed trap and the concentration of theorgano-metallic complex in the fuel before combustion is 30 ppm or less.5. The method according to claim 1 wherein the organo-metallic complexcomprises a complex of Na and/or K.
 6. The method according to claim 1wherein the organo-metallic complex comprises a complex of Sr and/or Ca.7. The method according to claim 1 wherein the organo-metallic complexis stable to hydrolysis.
 8. The method according to claim 1 wherein theorgano-metallic complex is fuel soluble.
 9. The method according toclaim 1 wherein the organo-metallic complex is soluble in afuel-compatible solvent to the extent of 10 wt % or more.
 10. The methodaccording to claim 9 wherein the organo-metallic complex is soluble inthe solvent to the extent of 25 wt % or more.
 11. The method accordingto claim 9 wherein the organo-metallic complex is soluble in the solventto the extent of 50 wt % or more.
 12. The method according to claim 1wherein the organo-metallic complex is derived from the reaction of analkyl or alkenyl succinic anhydride or its hydrolysis product with aGroup I or Group II metal hydroxide or oxide.
 13. The method accordingto claim 1 wherein the organo-metallic complex is dosed to the fuel atany stage in a fuel supply chain.
 14. The process for improving theoxidation of carbonaceous products derived from the combustion orpyrolysis of fuel, said process comprising the steps of:(a) adding tothe fuel before the combustion thereof a composition comprising as thesole organo-metallic complex an organo-metallic complex of a Group I ora Group II metal, wherein the concentration of the metal of the Group Ior the Group II organo-metallic complex in the fuel before combustion is100 ppm or less, and wherein the organo-metallic complex comprises analkali or alkaline earth metal salt of an alkyl or alkenyl-substitutedsuccinic acid, and thereafter (b) passing combusted gases through aparticulate filter trap thereby collecting the particles produced duringcombustion.
 15. The process as claimed in claim 14 wherein theconcentration of the metal of the Group I or the Group IIorgano-metallic complex in the fuel before combustion is 30 ppm or less.16. The process as claimed in claim 14 wherein the filter trap is aceramic monolith trap and the concentration of the metal of the Group Ior the Group II organo-metallic complex in the fuel before combustion is30 ppm or less.
 17. The process as claimed in claim 14 wherein thefilter trap is a deep bed trap and the concentration of the metal of theGroup I or Group II organo-metallic complex in the fuel beforecombustion is 30 ppm or less.
 18. The process as claimed in claim 14wherein the Group I organo-metallic complex comprises a complex of Naand/or K.
 19. The process as claimed in claim 14 wherein the Group IIorgano-metallic complex comprises a complex of Sr and/or Ca.
 20. Theprocess as claimed in claim 14 wherein the organo-metallic complex isfuel soluble.
 21. The process as claimed in claim 14 wherein theorgano-metallic complex is dosed to the fuel at any stage in a fuelsupply chain.